1. Field of the Invention
The present invention relates to a method for improving a high-speed downlink operation for a wireless communications system and related communications device, and more particularly to a method for improving a cell update procedure used for a high-speed downlink operation in a CELL_FACH state for a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the 3rd Generation Partnership Project (3GPP) provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency so as to improve uplink/downlink transmission rate.
On the basis of HSDPA, the 3GPP launches High Speed Downlink Shared Channel reception in CELL_FACH state, which is abbreviated to HS-DSCH reception in CELL_FACH state, and CELL_FACH state is well known as one of radio resource control (RRC) states. HS-DSCH reception in CELL_FACH state allows a user equipment (UE) monitoring the HS-DSCH for downlink data reception with cooperation of related control channel, namely Shared Control Channel for HS-DSCH (HS-SCCH), so as to improve peak data rate, signaling delay, state transition delay and flexible cell capacity.
A UMTS radio access network (UTRAN) enables HS-DSCH reception in CELL_FACH state by means of the system information broadcast, and related parameters correspond to HS-SCCH and HS-DSCH configuration and a common HS-DSCH radio network transaction identifier (Common H-RNTI).
The parameters corresponding to the common H-RNTI provides multiple common H-RNTIs values for the UE to select. For the UE in idle mode, the parameters are obtained from a “Downlink HS-PDSCH system information” information element (IE), included in a system information block (SIB) type 5/5bis. For the UE in the RRC connected mode, the parameters are obtained from a “Downlink HS-PDSCH system information for connected mode” IE, included in a SIB type 6. On the other hand, the UE includes a common H-RNTI variable for storing the selected common H-RNTI. Each common H-RNTI is shared by several UEs for grouping the UEs in the same cell, and also represents an identity of the UEs in the same group.
In addition to the common H-RNTIs, the UE may use a dedicated H-RNTI for HS-DSCH reception in CELL_FACH state. Each dedicated H-RNTI only represents the identity of a specific UE. Through an cell update procedure initiated by the UE, the UTRAN can determines to use a first function or a second function for allocating a dedicated H-RNTI to the UE or not.
When the UE reselects a new cell and settles in the cell, the UE has to initiate a cell update procedure and enter CELL_FACH state for notifying the UTRAN of related changes of the communications circumstance. The exchange of RRC messages related to the cell procedure is described as follows. Firstly, the UE sends a CELL UPDATE message to the UTRAN. In addition to cell reselection, several situations, such as radio link failure and an RLC unrecoverable error, also require the UE to initiate the cell update procedure. If the CELL UPDATE message notifies the UTRAN that the reason of procedure initiation is radio link failure, the UTRAN sends an RRC CONNECTION RELEASE message to indicate the UE to re-make an RRC connection. IF the procedure is initiated due to other reasons (i.e. cell reselection), the UTRAN sends a CELL UPDATE CONFIRM message via a dedicated control channel (DCCH) or a common control channel (CCCH). The CELL UPDATE CONFIRM message may includes different configuration data, and the UE feedbacks with different messages according to the configuration data, so as to perform radio bearer reconfiguration or releasing, mobile information update or transport channel reconfiguration.
If the UTRAN uses the first function for the cell update procedure, a New H-RNTI IE is set with a dedicated H-RNTI and then included in the CELL UPDATE CONFIRM message. On the other hand, the UE owns an H-RNTI variable for storing the settings of the dedicated H-RNTI. If the UTRAN uses the second function, no New H-RNTI IE is included in the CELL UPDATE CONFIRM message, and the UE continues using the original common H-RNTI.
The UE can activate or deactivate the HS-DSCH reception in CELL_FACH state by determining a HS_DSCH_RECEPTION_CELL_FACH_STATE variable. When the UE enters CELL_FACH state and also activates HS-DSCH reception, the UE uses the dedicated H-RNTI if the H-RNTI variable is set. Otherwise, the common H-RNTI is used. Thus, if the UE selects a new cell, the UE keeps using the common H-RNTI for HS-DSCH reception in CELL_FACH state.
For a transmission packet header, except for the headers mapped to HS-DSCH or enhanced dedicated channel (E-DCH), a media access control (MAC) layer defines five fields as follows: Target Channel Type Field (TCTF), C/T, UE Id, UE Id Type and MBMS Id. The UE Id and UE Id Type fields are both used for providing an identifier of the UE so that the UE can identify the packets belonging to it.
In the MAC layer of the UTRAN, a MAC-d protocol data unit (PDU) adopts different header formats based on the different transport channels, and thereby is formed into a MAC-d service data unit (MAC-d SDU).
In addition, a MAC-ehs PDU includes a plurality of concatenated MAC-d PDUs and is transmitted on HSDSCH. A header of the MAC-ehs PDU consists of Logic channel identity (LCH-ID), Length (L), Transmission Sequence Number (TSN) and Flag fields. In general, the MAC-ehs PDU is applied to the UE in CELL_DCH state for the HSDPA operation and thereby each UE has a dedicated H-RNTI. Therefore, the MAC-ehs PDU can be sent to the targeting UE without including any UE identity information.
In the prior art, the UE using the common H-RNTI has to identify the received MAC packets with the headers and thereby determines to discard the packets or take a next process for dissembling the packets. On the contrary, the UE using the dedicated H-RNTI does not need the packet-identifying step. However, as can be seen from the above, the UE Id and UE Id Type fields, which carry identifiers of the targeting UE/UEs, are included neither in the MAC-d PDUs nor in the MAC-ehs PDUs. In this situation, the UE, who uses the common H-RNTI for HS-DSCH reception in CELL_FACH state, has no way to identify the received MAC packets. Thus, the reception of the MAC packets in MAC-d PDUs is impossible.
In brief, the UTRAN of the prior art can use the first or second function during the cell update procedure, so as to manage the UE to use the dedicated or common H-RNTI for HS-DSCH reception in CELL_FACH state However, the UE using common H-RNTI fails in reception of MAC packets in MAC-d PDUs sent on the HS-DSCH.